The present invention relates to an improvement of an air conditioner used in electric vehicles.
An air conditioner used in electric vehicles is known which cools air by repeating gas compression and expansion in a circulative manner between a condenser and an evaporator via a compressor driven by a motor.
Generally, this type of air conditioner used in electric vehicles achieves a desirable cooling state by determining the rotation speed of the motor for driving the compressor by a controller (e.g., an A/C controller) based on a predetermined temperature set by a temperature setting switch for controlling the air condition, and by driving and controlling the motor to achieve that rotation speed.
However, when the cooling load is large, namely, when the outside air temperature is high where a great force is required for the compressor to compress gas, the load of the motor for driving the compressor is also increased, requiring a great amount of driving current for rotating the motor at the target rotation speed.
Of course, such an overload of the motor can be solved by using a motor with a larger rated current, but still there remains a problem of large current consumption. Specially for electric vehicles, this may deteriorate the running performance of the vehicle itself.
In addition, a large motor will also cause an increase in the cost for producing the vehicle.
In order to solve the above-mentioned problems, conventional air conditioners detect load on the compressor (i.e., detect a driving current of the motor for driving the compressor). When this value exceeds a predetermined value and an excessive amount of load is put on the motor, the target rotation speed of the motor is forcibly reduced, thereby preventing an excessive amount of current to be supplied to the motor to prevent excessive electric consumption and damage on the motor.
As a result, the compressor can no longer exert a rotation speed sufficient to maintain the desired cooling performance and thus results in a significant loss of cooling power of the air conditioner under a high temperature environment.
Thus, the present invention has an objective of solving the above-described problems to provide an air conditioner used in electric vehicles which can exert sufficient cooling performance without enlarging the size of the motor for driving the compressor or supplying an excessive amount of driving current to the motor for driving the compressor.
The present invention is an air conditioner used in an electric vehicle which cools air by repeating compression and expansion of gas in a circulative manner between a condenser and an evaporator via a compressor driven by a motor. In order to achieve the above-described objective, the air conditioner of the invention comprises: a condenser fan for cooling the condenser; a motor for driving the condenser fan; a load detector for detecting a load put on the compressor; and a rotation speed controller which increases the rotation speed of the motor for driving the condenser fan when the amount of the load detected by the load detector is relatively large, and decreases the rotation speed of the motor for driving the condenser fan when the amount of the load detected by the load detector is relatively small.
Due to this configuration, the rotation speed of the motor for the condenser fan will automatically be increased when the load put on the compressor becomes high in order to cool the condenser by the rotation of the condenser fan. Accordingly, the temperature of the gas inside the condenser is decreased and the load put on the compressor for compressing the gas as well as the load of the motor for driving the compressor are lightened. A rotation speed of the compressor necessary to achieve the temperature set for that time point can be obtained without supplying a high driving current to the compressor motor. Therefore, a sufficient cooling performance can be exerted without enlarging the size of the compressor motor or supplying an excessive amount of driving current to the same. Since the compressor motor is not damaged or the running performance of the electric vehicle is not deteriorated, comfort cooling is realized.
The load detector may comprise a current detector for detecting a driving current of the motor for driving the compressor, and the rotation speed controller may comprise a voltage adjuster for adjusting a voltage supplied to the motor for driving the condenser fan.
Since the driving current of the compressor motor is proportional to the load put on the compressor motor, the load put on the compressor can be determined by detecting the driving current. The rotation speed of the motor for driving the condenser fan can easily be controlled by adjusting the voltage applied to the motor for the condenser fan.
Preferably, the rotation speed controller judges the amount of load put on the compressor based on a reference current for judging the amount of load put on the compressor, and gives a command to the voltage adjuster to output a relatively high voltage when the driving current detected by the current detector is higher than the reference current or to output a relatively low voltage when the driving current detected by the current detector is lower than the reference current.
Due to this configuration, the voltage applied to the motor for the condenser fan is increased to increase the rotation speed of the condenser fan when the load put on the compressor becomes high and the driving current detected by the current detector becomes higher than the reference current. Accordingly, the temperature of the gas inside the condenser is reduced, and thus the load put on the compressor for compressing the gas as well as the load of the motor driving the compressor are lightened. Thus, the target rotation speed of the compressor motor necessary at that time point can be achieved without supplying an excessive amount of current to the compressor motor. On the other hand, the voltage applied to the motor for the condenser fan is reduced to decrease the rotation speed of the condenser fan when the load put on the compressor is low and the driving current detected by the current detector is lower than the reference current. As a result, useless electric consumption due to the motor for driving the condenser fan can be suppressed.
The rotation speed controller may store a plurality of different reference currents for judging the amount of load put on the compressor and a plurality of output voltages corresponding to current ranges separated by each of the reference currents, and may output a voltage corresponding to the current range that includes the driving current detected by the current detector.
In this case, the condenser fan can be driven at an appropriate rotation speed according to the load put on the compressor (i.e., the amount of the driving current of the compressor motor). Accordingly, the motor for driving the condenser fan is driven at a minimum rotation speed necessary at that time point. Thus, the rotation speed is optimized and needless electric consumption by the motor for driving the condenser fan can be prevented.
The output voltage corresponding to the current range separated by each of the reference currents may be 0 at minimum. In other words, the motor for the condenser fan may completely be halted where the load put on the compressor is significantly low.